Change over time
Seasonal subseries plot
Groups observations by seasonal position to compare repeated patterns across cycles.
- Plot
- Seasonality
- Trend over time
What it answers
Does the same season behave differently across cycles?
- Shape
- Grouped seasonal line segments
- What it shows
- Repeated seasonal effects and changing season levels.
Example
The question
Is each month’s sales level steady across years, or drifting?
Sales by month, 2021 to 2025, one panel per month (EUR million)
Illustrative data. It belongs to no company.
When to use it
Use it when
Separating seasonal position from year-to-year change.
Avoid it when
Too few cycles or irregular seasons without careful alignment.
How to read it
Compare observations within each seasonal group, then seasonal means.
The data you need
- Layout
- Long table
- Fields
- Cycle: year or cycle ID; Season: ordered month/quarter/etc.; Value: number
- One row is
- One seasonal position within a cycle. What is the grain?
- Rules
- Define the repeating cycle and season order. Do not sort month labels alphabetically.
- Optional
- Alternative: Date,Value with cycle and season derived from dates.
- Preparation
- Parse and sort timestamps or sequence positions; aggregate duplicates deliberately and preserve gaps. Define the repeating cycle and season order. Do not sort month labels alphabetically.
- Units
- Time uses a stated date/time unit and sampling period; the value axis uses the measure's unit. Rates need their own explicit denominator.
Worked example
Data Jan 2025=30, Jan 2026=38; Feb 2025=34, Feb 2026=40. Group months. January rises 8 across years.
| Year | Month | Value |
|---|---|---|
| 2025 | Jan | 30 |
| 2025 | Feb | 34 |
| 2026 | Jan | 38 |
| 2026 | Feb | 40 |